The best way to assure that you have round robin is to host the DNS yourself, I do exactly what you are trying to accomplish with 2 servers that are in different parts of the country. This is How I accomplish it...
Install BIND(named) 9.x.x it has round robin automatically.
Change your parent servers dns to just point at your nameserver, eg- NS1.EXAMPLE.COM and NS2.EXAMPLE.COM and define one of the DSL IP addy's for each.
Add a master zone for your TLD(top level domain) with a record that looks similar to this
Code:
$ttl 38400
example.com. IN SOA ns1.example.com whoever.example.com. (
1092506603
3700
3600
604800
38400 )
example.com. IN NS ns1.example.com.
example.com. IN NS ns2.example.com.
example.com. IN A first dsl connections ip address
example.com. IN A second dsl connections ip address
www.example.com. IN CNAME example.com.
ns1.example.com. IN A first dsl connections ip address
ns2.example.com. IN A second dsl connections ip address
this defines your TLD and your nameservers, and adds a canonical name for www. so
www.example.com will be directed to example.com
Now on failover or in the event of an outage if the clients browser does not get a reply from one IP it will automatically try the other.
Have fun,
linux_terror